The present invention relates generally to the field of reference pulse processing circuitry in which a reference pulse corresponding to the occurrence of a predetermined rotational position of a rotating shaft is received by a circuit and further processed. More particularly, the present invention is related to such a reference pulse circuit which is adaptable for control of an internal combustion engine.
In prior engine control systems it is known to sense the rotation of the engine crankshaft by sensing the passage of projections (teeth) present on a wheel rotated by the engine crankshaft. Typically, a large number of teeth are provided on the rotating wheel to provide crankshaft angular rotation resolution with the spacing between each tooth representative of a predetermined number of degrees of revolution of the engine crankshaft. These large number of teeth provide a means of monitoring the relative rotation of the engine crankshaft, but typically they do not provide information identifying one predetermined reference position of the crankshaft as opposed to other rotational positions. In some systems it is necessary to provide an indication of a reference position of the rotated wheel which is representative of a single reference rotational position of the engine crankshaft which occurs once for each crankshaft revolution. This reference position pulse is typically utilized to initiate proper sequential engine control and distinguish which one of the engine cyclinders should be receiving fuel and spark ignition at any particular time, whereas the large number of projecting teeth are utilized in determining the amount of fuel to be injected and the precise timing of the fuel injection and occurrence of spark in each engine cyclinder. Such systems are well known and include distributorless ignition systems and fuel injection systems such as those shown in U.S. Pat. Nos. 4,104,997, 4,338,813 and 4,338,903, all assigned to the assignee of the present invention.
Some prior engine control systems utilize one sensor to sense the passage of a large number of closely spaced teeth to provide precise resolution of engine rotation, while an additional separate sensor or the same sensor is utilized to sense either a specially shaped tooth or an extra one of the rotated teeth, a separate reference tooth rotated synchronously with the engine crankshaft. There are also a number of systems in which the engine crankshaft reference position is indicated by the occurrence of the absence of one of a large number of teeth on a rotating wheel wherein the remaining teeth provide pulses for the accurate angular resolution of engine crankshaft rotation.
In all of the prior systems, regardless of whether a specially shaped tooth, the absence of a tooth, or a separate sensor is utilized to sense a separate reference position projection, the occurrence of an erroneous reference position pulse is possible. The occurrence of a false reference pulse is actually quite likely in single sensor pulse detection systems during transient engine conditions such as abrupt engine acceleration and/or deceleration. While some engine control systems ignore pulse detections if they occur during certain conditions, such as dwell or spark, they do not insure the correctness of pulse detections at other times, and they do not insure that only true reference position pulses result in the implementation of engine control. If engine control is implemented in accordance with an erroneous reference position pulse, this can readily result in injecting fuel or initiating spark in an engine cyclinder at the wrong cycle time with the result being at least improper engine performance and possibly permanent engine damage.